Current Sensor (ACS712) Symbol
Definition: The Current Sensor (ACS712) symbol represents a Hall-effect-based linear current sensor integrated circuit manufactured by Allegro MicroSystems, shown in circuit diagrams with three functional pins — IP+ and IP− (current-carrying path) and VOUT (analog voltage output proportional to measured current) — used to measure AC or DC currents of 5A, 20A, or 30A with galvanic isolation between the current path and the signal output, following IEEE 315-1975 / ANSI Y32.2 rectangular IC symbol conventions.
Also known as: ACS712, ACS712ELCTR-05B, ACS712ELCTR-20A, ACS712ELCTR-30A, Hall-effect current sensor, linear current sensor IC, current transducer, non-invasive current sensor.
What the Current Sensor (ACS712) symbol means
The ACS712 symbol identifies a current sensing IC in a schematic where the measured current flows through the low-resistance internal conductor (IP+ to IP−) and the magnetic field generated by that current is sensed by an integrated Hall-effect element, producing an analog output voltage (VOUT) proportional to the current. Because the Hall element is electrically isolated from the current path, the ACS712 provides safe galvanic isolation between high-current circuits and sensitive microcontroller ADC inputs.
In circuit diagrams, the ACS712 symbol appears in power supply monitors, motor current feedback loops, overcurrent protection circuits, and energy measurement systems. The VOUT pin delivers a voltage that is 2.5V at zero current (offset reference) and changes by a fixed sensitivity factor (66mV/A for 5A, 100mV/A for 20A, or 66mV/A for 30A variant) for positive or negative currents.
How to identify the Current Sensor (ACS712) symbol
The ACS712 symbol is drawn as a rectangle with two current-path pins on the left (IP+, the current-in terminal, and IP−, the current-out terminal) and the signal output on the right (VOUT). Some schematic representations also show VCC and GND supply pins. The part number 'ACS712' or the full variant designation (e.g., ACS712ELCTR-20A-T) is printed beside or inside the block. An optional filter capacitor (100nF) is often shown on VOUT to GND in the surrounding circuit.
Function in a circuit
The ACS712 current sensor uses a precision Hall-effect transducer integrated on the same chip as a copper current path (IP+ to IP−, typical resistance 1.2mΩ). Current flowing through the copper conductor creates a proportional magnetic field; the Hall element converts this field to a differential voltage that is amplified and conditioned to produce a ratiometric analog output at VOUT. Output voltage = 2.5V + (sensitivity × current), where 'sensitivity' is variant-dependent (66mV/A, 100mV/A, or 66mV/A for 5A, 20A, 30A versions). The output is valid for both positive (IP+ to IP−) and negative (reverse) current flow, enabling bidirectional current measurement with a single-supply microcontroller ADC.
Standards: IEC vs ANSI
| IEC 60617 | The ACS712 is a proprietary Allegro MicroSystems device; its schematic symbol follows IEC 60617-12 rectangular block conventions for analog sensor ICs. No specific IEC symbol standard exists for Hall-effect current sensors; the rectangular block with labelled pins is used. |
|---|---|
| ANSI/IEEE 315 | The ACS712 symbol follows IEEE 315-1975 / ANSI Y32.2 rectangular IC symbol conventions. The reference designator 'U' is used for the IC, and an adjacent current arrow or annotation may indicate the direction of measured current. |
| Key difference | Both IEC and ANSI/IEEE representations use the same rectangular block; IEC schematics may use a functional qualifier label, while ANSI/IEEE schematics rely on the part number for identification. No functional difference between the two symbol styles. |
Terminals / pins
| Pin | Name |
|---|---|
| ip_pos | IP+ |
| ip_neg | IP- |
| vout | VOUT |
Typical values
Supply voltage: 4.5V–5.5V (VCC). Quiescent output voltage: 2.5V (at 0A, VCC = 5V). Sensitivity: 185mV/A (5A version), 100mV/A (20A version), 66mV/A (30A version). Current range: ±5A, ±20A, or ±30A. Internal conductor resistance: 1.2mΩ typical. Bandwidth: 80kHz (-3dB). Isolation voltage: 2.1kVRMS. Operating temperature: -40°C to +85°C.
Where the Current Sensor (ACS712) symbol is used
- Motor current monitoring in DC motor controllers and variable-frequency drives for overcurrent protection
- Battery charge/discharge current measurement in BMS (Battery Management Systems) for Li-ion packs
- Home energy monitors measuring AC mains current draw of appliances
- Solar charge controller current sensing for PV panel output and battery charging current
- Arduino and ESP32-based power monitors reading current via ADC for data logging
- Overcurrent detection and protection in switch-mode power supplies
- Industrial automation systems monitoring conveyor motor loads for fault detection
Example
In an Arduino motor driver circuit, the ACS712 symbol (20A variant) is placed in series with the motor supply rail — IP+ connects to the motor driver positive supply and IP− to the motor load return; VOUT connects through a 100nF filter capacitor to Arduino analog pin A0. The Arduino reads the ADC value, converts it using (voltage − 2.5) / 0.1 = current in amps, and triggers a relay to disconnect the motor if current exceeds 15A — the ACS712 symbol on the schematic immediately identifies the current sensing and galvanic isolation point.
Key facts
- The ACS712 symbol represents a Hall-effect linear current sensor IC that measures AC or DC current with galvanic isolation, providing an analog voltage output (VOUT) proportional to the measured current.
- VOUT = 2.5V at zero current (VCC = 5V), increasing or decreasing at a fixed sensitivity: 185mV/A (5A), 100mV/A (20A), or 66mV/A (30A) for the three standard variants.
- The IP+ and IP− pins carry the measured current through a 1.2mΩ internal copper conductor; the Hall element measures the resulting magnetic field without electrical contact to the current path.
- Galvanic isolation of 2.1kVRMS separates the high-current circuit (IP+/IP−) from the microcontroller signal output (VOUT), protecting sensitive electronics from transients.
- The ACS712 measures bidirectional current: positive current (IP+ to IP−) produces VOUT above 2.5V; negative (reverse) current produces VOUT below 2.5V.
- A 100nF low-pass filter capacitor between VOUT and GND is recommended in the Allegro datasheet to reduce output noise and bandwidth to the application's requirements.
- The ACS712 symbol is drawn per IEEE 315-1975 / ANSI Y32.2 as a rectangular IC block with designator 'U' and labelled functional pins IP+, IP−, and VOUT.
Frequently asked questions
What does the ACS712 current sensor symbol mean in a circuit diagram?
The ACS712 symbol means a Hall-effect current sensor IC is installed at that point. Current flows through the IP+ to IP− conductor path; the IC outputs an analog voltage (VOUT) proportional to that current. The 2.5V quiescent output represents zero current, with sensitivity of 100mV/A (20A version) or 185mV/A (5A version) above or below 2.5V.
What does the ACS712 symbol look like?
The ACS712 symbol is a rectangle with IP+ and IP− pins on the left (the high-current measurement path) and VOUT on the right (analog signal output). VCC and GND supply pins are also present. The part number 'ACS712' or the full variant code (e.g., ACS712ELCTR-20A) is written beside the block, and the designator 'U' identifies it as an IC.
How do you calculate current from the ACS712 output voltage?
Current (A) = (VOUT − 2.5) / sensitivity, where sensitivity is 0.185V/A for the 5A version, 0.100V/A for the 20A version, and 0.066V/A for the 30A version. For example, if VOUT = 3.5V with the 20A version: current = (3.5 − 2.5) / 0.1 = 10A flowing in the positive direction (IP+ to IP−).
How many pins does the ACS712 symbol have?
The ACS712 symbol has three functional signal pins: IP+ (current input), IP− (current output), and VOUT (analog voltage output). The physical SOIC-8 package also includes VCC (5V supply) and GND, giving five electrical connections. Pin numbers 1–4 are the current path (two pairs, bonded internally) and pin 8 is VCC, pin 7 is IP−, pin 6 is IP+, and pin 5 is VOUT in the SOIC-8 pinout.
What is the difference between the ACS712 5A, 20A, and 30A variants?
The three variants measure different current ranges (±5A, ±20A, ±30A) and have different output sensitivities: 185mV/A (5A), 100mV/A (20A), and 66mV/A (30A). Higher sensitivity means better resolution for small currents but a smaller measurement range. The 5A version is best for precision measurement of low currents; the 30A version suits high-current motor or power supply monitoring.
Does the ACS712 provide galvanic isolation?
Yes. The ACS712 provides 2.1kVRMS galvanic isolation between the current-carrying path (IP+/IP−) and the signal output (VOUT). This isolation protects microcontrollers and other low-voltage signal electronics from the high-voltage or high-current circuit being measured.
What is the quiescent output voltage of the ACS712 at zero current?
The quiescent output voltage (VQ) of the ACS712 at zero current is 2.5V when supplied with 5V VCC, which is exactly half the supply voltage. Any deviation from 2.5V in the output voltage represents a measured current: voltages above 2.5V indicate current flowing IP+ to IP−, voltages below 2.5V indicate reverse current flow.
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